It is usual to provide said mixtures by a mechanical kneading operation, notably with a blade agitator of mixer driven in rotation in the bowl containing the mixture. It has also been proposed, for eliminating from the mixture the gaseous inclusions, to evacuate the bowl during the kneading operation.
FR-A-1 473 563 which relates to the same technical field proceeds, in a first chamber, to a kneading operation under vacuum, then for improving the elimination of the gas pockets and the homogenizing, transfers the mixture to a second chamber in which the paste is simultaneously subjected to mechanical vibrations and to vacuum. It is in fact known, notably in the technique of concretes, that vibrations improve the homogeneity of pastes.
Said known method of preparing a paste under vacuum, which carries out the kneading operation in a first enclosure and the vibrations in a second enclosure has many practical disadvantages such as notably the necessity of a transfer from one enclosure to the other during the preparation process. It also has other disadvantages with regards to the homogeneity of the mixture and the presence in the final mixture of very small gaseous pockets.
The first of said disadvantages is due to the fact that the mixer or kneader has dead areas, notably the surface layer adhering to the bowl wall and to the blades of the kneading device, areas where no mechanical kneading of the paste is taking place. The second of said disadvantages results from the small amplitude of the mechanical vibrations, which is insufficient for providing a circulation of the fine gaseous bubbles causing a coalescence which increases their volume in such manner that a sufficient lift is imparted to them, notably in a viscous paste.